Multivibrator circuits



Feb. 18,1947. w, N L TA 2,416,201

' ,MULTIVIBRATOIR 'CIRCUIT Filed Oct. 22,1942

WITNESSES: I INVENTORS.

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ATTORNE Patented Feb. 18, 1947 MULTIVIBRATOR CIRCUITS George W. Nagel, Catonsville, and Mortimer A.

Schultz, Baltimore, Md, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 22, 1942, Serial No. 462,999

2 Claims.

Our invention relates to multivibrator electrical discharge tube circuits and, in particular, to multivibrator circuits which maintain a stable frequency of periodic discharge little affected by Variations of certain circuit constants, such as the supply voltage. Our multivibrator is particularly adapted to use in circuits to produce a periodic voltage having a frequency which is a sub-multiple of the frequency of an impressed periodic voltage. Such circuits may be termed frequencydividers and. their function be termed frequencydivision.

One object of our invention is to provide a multivibrator circuit which shall produce periodic electrical vibrations of a frequency which is substantially constant.

Another object of our invention is to produce a frequency divider which is capable of maintaining a ratio of the derived frequency to the impressed frequency which is a very constant fraction, and in which the constancy of this fraction is maintained notwithstanding Variations of supply circuit voltage, environment temperature, emissivity of the cathodes and the like.

Still another object of our invention is to produce a circuit of the multivibrator type in which the ratio of frequency division is a very small fraction.

Other objects of our invention will become apparent from the following description when taken in connection with the single figure of the drawing which is a schematic showing of one form of circuit embodying our invention.

It is desirable for many purposes in the electrical art to derive from a current which varies periodically at a high rate another current which varies periodically at a lower rate, and in which this lower rate is a very constant and exact submultiple of the rate of the higher frequency. One of the expedients for effecting this purpose is to impress upon the grid of one tube of a pair of tubes connected into a multivibrator circuit the higher frequency, and to derive a current having a submultiple frequency from the output circuit of the multivibrator, provided the circuit parameters, such as supply voltage, environment temperature. cathode emissivity and the like, remain constant and unaltered. A multivibrator circuit of the prior art type just referred to would be similar to that illustrated in the present drawmg were the bias battery omitted or made of small value and were the value of the cathode resistor only a small fraction of the value to be specified in the following description, this being more fully pointed out below.

We have found, however, that, when certain of the circuit parameters, for example, the value of the direct-current voltage applied to the anodes of the two tubes, undergo relatively small variations, considerable variation takes place in the frequency of the output current. In other words, the circuit does not give an output frequency which is a constant submultiple of the input frequency.

We have discovered that it is possible to remedy this defect of the prior art circuit by greatly increasing the value of the resistor interposed in the common lead from the cathode of the two tubes to the direct-current source of plate voltage,-

and by providing a high positive bias for the grids of the two multivibrator tubes. Thus, referring to the drawing, two electricaldischarge tubes I and 2, which may be of the high-Vacuum type embodying electron emissive cathodes 3 and. 4, control electrodes 5 and 0, and anodes I and 8, have their cathodes connected to ground through a common resistor 9. 'The anodes I and 8 are respectively connected to the positive terminal of a direct-current source II through resistors I2 and I3, respectively, the negative terminal of the source I I being connected to ground. The anode l is connected through a capacitor I4 to the grid 6 of the tube 2; and the latter grid is connected to one terminal of a resistor I5. The grid 5 is connected through a resistor I'I to the other terminal of the resistor I5. As already stated, the circuit so far described would be that of multivibrators of the prior art if the common terminal of the resistors I5 and I! were grounded, or connected to a low bias voltage. Instead of grounding the last-mentioned terminal directly, we connect it to the positive terminal of a direct-current source I8 ofwhich the negative terminal is grounded. We furthermore deviate from previous practice by making the resistor 9 from twenty-five to eighty times as large in value as was customary in multivibrators of the prior art. 0

To give one typical illustration of a practical circuit embodying our invention, the tubes I and Zmay be high-vacuum triodes of the type 6N7, now commonly sold on the market. The resistor 0 may have a value of 25,000 ohms or even more; the voltage source I I may have a terminal voltage of volts; the resistor I2 may have a value of 40,000 ohms; the resistor I3 may have a value of 0.5 megohm; the capacitor I 4 may be of .01 microfarad capacity; the resistor I! may have a value of 20,000 ohms; and the resistor I5 may have a value of 40,000 ohms. The source I8 may impress 55 volts positive on the common terminal of the resistors 15 and i1 relative to ground. This arrangement in itself is a multivibrator capable of producing output current derived from the resistor 9 or an output voltage waveform between anode 8 and the cathode 4 which is of constant frequency and waveform. Where it is desired to use this multivibrator to derive a voltage which is a constant submultiple of some higher frequency voltage, the circuit constants are arranged in accordance with principles well known in the art to generate an output frequency slightly less than the desired submultiple frequency, and the higher frequency which it is desired to subdivide is coupled, for example, through a capacity coupling, between ground and the control electrode 5.

If desired a capacitor 16 may be comiected between anode 8 and the common terminal of resistors l5 and H.

We claim as our invention:

1. In combination, a pair of tubes, each embodying a cathode, a control electrode and an anode, the two cathodes being connected through a common resistor of at least 20,000 ohms to the negative terminal of a directcurrent source of which the positive terminal is connected through a pair of resistors, respectively, to the two anodes of the tubes, a capacitor connected between the anode of the first tube and the control electrode of the second tube, a pair of resistor elements serially connected between the control electrodes of the'two tubes, and a source of bias voltage connected to impress a positive potential of at least 45 volts between the negative terminal of the direct-current source'and the common terminal of the two last-mentioned resistors.

2. In combination, a pair of tubes, each embodying a cathode, a control electrode and an anode, the two cathodes being connected through a common resistor to the negative terminal of a direct-current source of which the positive terminal is connected through a pair of resistors, respectively, to the two anodes of the tubes, a capacitor connected between the anode of the first tube'and the control electrode of the second tube, a pair of resistor elements serially connected between the control electrodes of the two tubes, and a source of bias voltage connected to impress a positive potential between the negative terminal of the direct-current source and the common terminal of the tWo last-mentioned resistors, the first-mentioned resistor being not less than onehalf as large as one of the two lastimentioned resistors.

' GEORGE W. NAGEL.

MORTIMER A. SCHULTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS White Jan. 2, 1940 

